1. Technical Field
The invention relates to a sliding bearing based on fiber-reinforced plastic with a plastic matrix and a plastic thread as reinforcing element. It also relates to a sliding element with such a sliding layer.
2. Related Art
The use of composite fiber materials for sliding bearings, in particular wound plastic sliding bearings based on epoxy resins, is of prior art. Such sliding bearings consist of a single-layer sliding layer material or a bearing material constructed from two layers, a support layer and a sliding layer. The sliding layer may be located on the inside relative to the support layer, according to the application. The support layer is typically characterised by a glass fiber or carbon fiber reinforced epoxy resin matrix which has a very high load absorption capacity. The sliding layer consists in most cases of special plastic fibers or threads of varying abrasiveness as reinforcing elements, solid lubricants and also of an epoxy resin matrix. The composition is set so that the required tribological properties are also set, which vary according to the material and condition of the counter-rotating element and the ambient conditions (wet or dry running).
The use of PTFE (polytetrafluoroethylene) or graphite, among other things, as a solid lubricant for the self-lubricating sliding layer, is of prior art. These substances are either added to the plastic matrix in particle form or, in the case of PTFE, are intertwined in the form of a filament with other plastic filaments to form the plastic thread of the sliding layer. As is well known, polyester is generally used as the thread plastic in most cases. Typically two polyester and one PTFE filament are intertwined to form a thread.
Both the sliding layer and the support layer of the sliding element are produced by winding the synthetic resin impregnated plastic thread or the synthetic resin impregnated glass fiber onto a rotating mandrel (winding core). The pipes with a circular cross-section thus produced are further processed into cylindrical bushes, semicircular bearing bushes and the like.
Although the use of PTFE as a solid lubricant has proved satisfactory in fiber reinforced plastic sliding layers due to its good sliding friction properties, tribological and mechanical properties not yet satisfactory for all applications have been achieved. For PTFE is highly reaction inert, because of the strong intermolecular binding of the carbon and fluorine atoms, and has a very low surface tension. Therefore no chemical reaction, or no appreciable reaction, takes place between the plastic matrix and the PTFE. It was established, particularly when the prior art plastic threads of two polyester filaments and one PTFE filament were used, that the PTFE filaments only reached a very adhesion to the plastic matrix. Consequently the sliding layers of prior art could not be re-machined mechanically without difficulty, or not at all. In most cases the result was delamination of the sliding layer and deterioration in the tribological properties and in the wear resistance of the siding layer.